Process for formation of dialkali metal dimers of diolefins



States PROCESS FOR FGRMATION F DIALKALI METAL DIMERS OF DIOLEFINS atent molecule than a dimer of the diolefin subjected to reaction with sodium under the described reaction conditions. In conclusion, the aforesaid patent does not disclose a process wherein a diolefin is selectively dimerized 5 to give individual derivatives, i. e., diacids, in a high degree of purity. Virgil L. Hansley and Stuart Schott, Cincinnati, Ohio, assignors to National Distillers and Chemical Corpora- Order 3 determine the effectiveness. of the said patent disclosure as to the preparation of dialkali tion, a corporation of Virginia metal derivatives of dimers by reacting a diolefin (e. g., No Drawing. Application December 30, 1955, butadiene) with an alkali metal (a. g., sodium), exten- Sellal 556,469 sive studies have been made of the process and products 8 Claims (CL 260 665) obtained therefrom. Specifically, and in the manner described in the specific example in the aforesaid patent, butadiene has been subjected to reaction at about 0 C. The present invention relates to a process for prod'ucwith a substantial excess of sodium in the presence of tion of dimerized products from diolefins and, more parethylene glycol dirnethyl ether or dimethyl ether with ticularly, to a process wherein a conjugated aliphatic the solid sodium surface 'being continually abraded durdiolefin is reacted with an alkali metal to produce, in ing the reaction by forcing the sodium against a wire selective manner and high yields, dimerized products of brush. The conditions under which the studies were carthe diolefin. More specifically, the invention relates to ried out and the results obtained are set forth in the folan improved process wherein an aliphatic conjugated dilowing tabulation and include results obtained with simulolefin such as butadiene, is selectively dimerized in the taneous or subsequent carbonation of the reaction prodpresence of a finely divided alkali metal, such a sodium, uct. For each run, the product of the carbonation reto produce in selective manner and in high yields :a mixaction was acidified and distilled to determine the yield, ture of disodiooctadienes. if an, of distillable acids which would include diacids In the prior art, numerous disclosures are available corresponding to acids of 2 more carbon atoms per pertaining to the use of alkali metals for carrying out molecule than a dimer of butadiene if the process was various types of reactions in which organo-alkali metal effective in producing disodiooctadienes convertible to intermediates and derivatives thereof are prepared. For C dlaclds.

Reaction Conditions Product Analysis Fiercest 1e Run No. Sodium, Per- Butadiene Oarbonation Distillable Neutralon Bucent Excess Solvent; Min acids, ization tadiene over grams Equivatheory Grams Rate lent 1 1 1,000 Ethylene glycol dimethyl 107 all at start 138 separate step, 0.627 g. Trace ether. (JO /mm. 1,000 d 216 separate step, Dry Ice... do 1,000 dimethylether i. 252 do 5.4 1,000 do 250 simultaneous, CO2 5.5

1 The theoretical neutralization equivalent for 010 aliphatic unsaturated dibasic acids corresponding to diacids of two more carbon atoms than dimers of butadiene=99.

2 The major product from the butadiene was white, polymeric rubber acids.

example, it has been heretofore proposed, as in U. S.

As is apparent from the foregoing data, which is also Patent No. 2,352,461, to prepare mixtures of organic disclosed in co-pending application S. N. 382,456, filed acids by reacting an aliphatic diolefin such as butadiene, with sodium or potassium and carbon dioxide in a special solvent and to hydrolyze the compounds so obtained. This patent discloses the use of sodium in massive form (i. e., sodium strips) for carrying out the described reaction with or without provision for abrading or scraping the sodium surface, such as with a rotating brush or scraper, to remove continuously encrustations from the sodium and expose fresh surfaces of the metal. The aforesaid patent describes, with a series of chemical equations, one possible mechanism whereby, by reaction of an olefin such as butadiene with sodium and carbon dioxide in a selected ether medium, products are September 25, 1953, the process disclosed in aforesaid patent No. 2,352,461 fails to produce other than a trace or exceptionally small amount of distillable acids (maximum of about 2%), the major part of the butadiene reactant having been converted to high molecular weight rubbery products. Moreover, it is further apparent from the foregoing data that, in the trace or small amounts of distillable acids produced, no substantial, if any, amount of C aliphatic diacids derived from dimers of butadiene are contained therein, since the neutralization values obtained for the distillable acids as compared to the theoretical neutralization equivalent of such C diacids (N. E. 99) negates any substantial attainment of such acids by practice of the patented process.

In further studies carried out to determine the efliectiveness of a process as disclosed in U. S. Patent No. 2,352,461 for preparation, by reaction of sodium with butadiene, of aliphatic diacids corresponding to diacids having two more carbon atoms per molecule than dimers of butadiene, the reaction was carried out with use, instead of sodium in massive form, of a 50% sodium dispersion (hereinafter designated as a Normal dispersion) in mineral spirits in which the particle size characteristics f the sodium were determined by visual examination with a microscope having a calibrated eyepiece.

Average particle size About 12 microns. Maximum particle size About 30 microns. Percent of particles of about microns or less Not more than about 10. Percent of particles above about microns Do.

The reaction studies with use of sodium in a Normal dispersion of the defined particle size characteristics were carried out by adding the sodium dispersion (1.1 gram atom of sodium) in mineral spirits to 3 liters of dimethyl ether in a stirred reactor. Butadiene (1 gram mole) was passed into the reactor with stirring over a minute period at a temperature of about C. The product obtained from the reaction of butadiene with the sodium was subjected to carbonation by pouring the reaction product onto an excess of Dry Ice, the carbonated product was then acidified with hydrochloric acid, and the acidified product was distilled. Analysis of the distillate failed to reveal the presence of C aliphatic unsaturated diacids as would be obtained if the process was elfective in producing disodio dimers of butadiene which, upon carbonation and acidification, result in C unsaturated diacid precursors (before hydrogenation) of C saturated acids such as sebacic acid, 2-ethylsuberic acid, and 2,2- diethyladipic acid.

Thus, as illustrated by the foregoing data, use of (1) bulk sodium (with abrasion during reaction) or (2) sodium in as finely dispersed form as is defined hereinbefore for the Normal dispersion for reaction with butadiene in the presence of the defined ether reaction medium did not effect substantial, if any, dimerization of butadiene whereby to produce sodium derivatives (e. g., disodiooctadienes) convertible to C aliphatic diacids upon carbonation and acidification of the carbonated product.

Although reaction of an aliphatic conjugated diolefin such as butadiene, in the presence of the selected ether reaction mediums, with an alkali metal such as sodium in bulk form or in the form of a dispersion of sodium particles as fine as aforedefined for the Normal dispersion results in no substantial, if any, production of dimerized butadiene derivatives convertible to C diacids, the reaction with use of such Normal dispersions can be carried out with selective high yields of desired disodiooctadienes carbonatable to salts of C aliphatic diacids by processes described in co-pending applications S. N. 333,354, filed January 26, 1953, now abandoned; S. N. 382,456, filed September 25, 1953, and S. N. 398,218, filed December 14, 1953. As disclosed in the co-pending applications, selective production in excellent yields of the desired dialkali metal derivatives of the diolefin dimers is obtained by carrying out the reaction between the diolefin and alkali metal as a Normal dispersion, in the presence of an active ether reaction medium and in the presence of a small amount of an activating agent such as a polycyclic aromatic hydrocarbon and/or in the presence of a suitable attrition agent. In particular, S. N. 382,456 discloses data showing that when a Normal sodium dispersion of 5-l5 micron average size is employed in combination with the polycyclic aromatic hydrocarbon, excellent yields on the order of 8090% of the desired acids are obtained, based on the butadiene reactant. Similarly, S. N. 398,218 discloses the selective production in high yields of the desired dimer products with the use of the Normal finely dispersed alkali metal in presence of a suitable attrition agent.

Although the processes described in the aforesaid copending applications provide particularly effective methods for reacting a conjugated aliphatic diolefin with an alkali metal to produce selectively and in high yields dialkali metal derivatives of the diolefins, desiderata are the production of such derivatives in selective manner and in high yields with minimization of the number of required ingredients in the mixture undergoing dimerization and facilitation of subsequent handing operations, which are complicated by the presence of certain ingredients, in the: conversion of the reaction product to, and recovery of, desired valuable derivatives of the dimerized product. For example, desiderata include the provision of a method for reacting a conjugated diolefin with an alkali metal under conditions for selective production in high yields of dialkali metal derivatives of the diolefin dimers without need for use of any activating agents, attrition agents, and the like, thereby simplifying the entire process by substantial reduction in the number of ingredients required and thereby obviating problems associated with the presence of activating agents, etc. in the preparation and recovery of the dialkali metal dimers and/or desired derivatives thereof.

It is the primary object of this invention to provide a method for selective production in high yields of dialkali metal derivatives of diolefin dimers by reacting an aliphatic conjugated diolefin with an alkali metal in improved manner whereby the desiderata aforedefined are obtained. Although the process embodied herein, and described more fully hereinafter, does not preclude the use, if desired, of activating agents and attrition agents such as are disclosed in the aforesaid co-pending applications, the process embodied herein can be carried out without need for use of such agents with obtainment of at least comparable yields of the desired dimerized products and obtainment of other advantages including the avoidance or substantial minimization of the tendency for the alkali metal to agglomerate during the reaction with the olefin.

It has now been discovered that an aliphatic conjugated diolefin can be reacted with an alkali metal in the presence of a selected reaction medium to produce, in selective manner and in high yields, dialkali metal derivatives of dimers of the diolefin if the alkali metal reactant is employed in the form of a dispersion in which the particle size characteristics of the dispersed alkali metal fall within rather well defined limits of size characteristics. As is apparent from the description set forth hereinafter, average particle size characteristics of the alkali metal dispersion is not necessarily the sole factor which enables carrying out the invention as, over and above average size characteristics, it is essential that the alkali metal dispersion contain in excess of a rather well defined amount of relatively low size characteristics. Thus, as will be apparent from the specific embodiments used hereinafter for further describing the invention, the desired dimerization reaction can be effected by use of an alkali metal dispersion of particle size characteristics as embodied for use herein whereas the desired dimerization may not be effected by use of an alkali metal dispersion which, though it may be of comparable average particle size characteristics, does not contain the rather well defined amount of particles of controlled size characteristics required for practice of the present invention.

Generally speaking, the process embodied herein comprises reacting an aliphatic conjugated diolefin, in the presence of a suitable reaction medium, with an alkali metal in dispersed form in which more than about 30% of the alkali metal particles are of less than about five microns in size, and more preferably, not more than about three microns in size, under conditions whereby there is produced in selective manner high yields of dialkali metal derivatives of dimers of the diolefin. More preferably, the process embodied herein is carried out by use of the alkali metal in the form of a dispersion in which more than about 30% of the alkali metal particles are of less than about five microns in size, and more preferably, not over about three microns, and the average particle size of the dispersion is not more than about ten microns. In a still more preferred embodiment, the invention is carried out by use of the alkali metal in the form of a dispersion in which (a) more than about 30% of the alkali metal particles do not exceed about three microns in size,-

(b) the average particle size of the dispersion averages not more than about one micron and (c) the dispersion is devoid of more than about of alkali metal particles larger than about fifteen microns in size. Optimum results are generally obtained by use of an alkali metal dispersion in which all or substantially all of the alkali metal particles do not exceed about three microns in size and the average particle size is less than 1 micron in diameter.

For carrying out the process embodied herein, suitable examples of the alkali metal include sodium, potassium and lithium with sodium being preferred as it provides for excellent selectivity and yields of desired dimerized products and is cheaper and more readily available. Use of chemically pure sodium is not essential, however, as mixtures containing a substantial amount of sodium are useful as are alloys of sodium and potassium, of sodium and calcium, and of sodium and lithium.

The diolefins which are useful for this improved process include any aliphatic conjugated diolefin including, for example, butadiene, isoprene, dimethyl butadiene, the pentadienes, as the methyl-1,3-pentadienes, and the like. In general, it is desirable to use the aliphatic conjugated diolefins having from 4 to 8, inclusive, carbon atoms.

The reaction medium found most suitable consists essentially of an ether and only certain types of ethers are effective. The ether can be any aliphatic mono ether having a methoxy group, in which the ratio of the number of oxygen atoms to the number of carbon atoms is not less than 1:4. Examples include dimethyl ether, methyl ethyl ether, methyl n-propyl ether, methyl isopropyl ether, and mixtures of these methyl ethers. Certain aliphatic polyethers are also quite satisfactory. These include the acyclic and cyclic polyethers which are derived by replacing all of the hydroxyl hydrogen atoms of the appropriate polyhydric alcohol by alkyl groups. Typical examples are the ethylene glycol dialkyl ethers such as the dimethyl, methyl ethyl, diethyl, methyl butyl, ethyl butyl, dibutyl, and butyl lauryl ethylene glycol ethers; trimethylene glycol dimethyl ether, glycerol trimethyl ether, glycerol dimethyl ethyl ether, and diethylene glycol methyl ethyl ether, dioxane, glycol formal, methyl glycerol formal, and the like, as well as ethyl and methyl ortho formates, methylal and acetals having the proper carbon to oxygen ratio. The simple methyl monoethers, as dimethyl ether, and the polyethers of ethylene glycols, as ethylene glycol dimethyl ether are preferred. Hydrocarbon solvents such as isooctane, kerosene, toluene, and benzene cannot be used exclusively as reaction media since they adversely affect the dimerization reaction and give little or no yield of dimer products.

The ethers should not contain any groups such as hydroxyl, carboxyl, and the like which are distinctly reactive towards sodium. Although the ether may react in some reversible manner, it must not be subject to cleavage to give irreversible reaction products during the dimerization process. Such cleavage action destroys the ether and introduces into the reacting system metallic alkoxides which, in turn, tend to induce the rubber forming reaction with the diolefin rather than the desired dimerization reaction.

Although the reaction medium should consist essentially of the specified ethers, other inert media can be employed in limited amounts. In general, these inert media will be introduced with the alkali metal dispersion as the vehicles in which the alkali metal is suspended. They have the principal effect of diluting the ethers. As the effective concentration of the active ether is decreased by the increased addition of inerts, a minimum concentration of ether is reached below which the promoting effect is not evident. The exact minimum concentration depends upon the particular reactants and ether being used as well as the reaction conditions, such as temperature,

reactant concentration, and the like employed. In any event, the concentration of ether in the reaction mixture should at all times be maintained at a sufficient level to have a substantial promoting effect upon the dimerization reaction. In general, it is good practice to use a reaction medium having at least 50 weight percent of active ether. Although the amount may be varied considerably, from to 2000 cc. of the ether per mole of diolefin undergoing reaction has been found satisfactory.

In preparation of the alkali metal dispersion, it is desired to employ at least one or more dispersing agents capable of promoting rapid and complete breakdown of the gross sodium particles. Choice of these dispersing aids is important, although a number of different selected materials can be used. In one system, copper oleate is used for maximum rapid particle breakdown, and dimer acid for maximum dispersion stability. Aluminum stearate, as well as other selected metallic soaps have also been found to function quite satisfactorily. For optimum flow characteristics of the initial dispersion, other materials can also be used either alone or in combinations. Dispersing aids which are useful include dimer acid, oleic acid, aluminum stearate, aluminum octanoate, calcium stearate, aluminum laurate, lead naphthenate, zinc stearate and other metallic soaps as well as lecithin, polymers, rubbers, etc.

In practice of the process embodied herein, the reaction temperature is preferably held below 0 C., and more preferably, between 20 C. to -50 C. as generally speaking, all ethers begin to yield cleavage products at temperatures of about 0 C. and above with the result that sufiicient alkoxides are formed to yield high polymeric acids rather than the desired low molecular weight dimers. However, and depending on the particular reaction medium employed, the reaction may be carried out at somewhat higher temperatures, with or without use of pressure, such as up to about 30 C., but use of the higher temperatures are generally not preferred as the yield of desired products tends to decrease as the temperature is increased over about 0 C.

The process embodied herein may be carried out in batch-wise, semi-continuous or continuous manner and it is not intended to be limited to any particular method of operation. For example, the reaction may be carried out in a stirred reaction vessel in which the ether reaction medium and alkali metal dispersion are maintained at desired temperature (e. g., below about 0 C.) and the diolefin reactant introduced either as a gas, or as a liquid. One quite satisfactory method is to introduce the diolefin into the reaction vessel at approximately the same rate at which it reacts with the alkali metal. Using finely dispersed alkali metal, it is usually suitable to employ only an equimolar amount with the olefin to be reacted. The dimetallic derivatives of the diolefin dimers which are selectively formed are thus produced in the reaction mixture. These products, depending on the diolefin used, may be either soluble or insoluble in the reaction medium. In general, they tend to form slurries, as for example, the disodiooctadienes produced from sodium and butadiene.

These dimetallo derivatives can either be isolated as such or directly and immediately thereafter subjected to further reactions to form valuable derivatives. For example, subsequent carbonation of the mixture containing the products yields the salts of dicarboxylic acids. The carbonation may be carried out by subjecting the dimetallo derivatives to dry, gaseous carbon dioxide, by contact with solid carbon dioxide or by means of a solution of carbon dioxide. The temperature for carbonation is preferably controlled below about 0 C. to avoid the formation of unwanted by-products. The carbonation forms the dimetallic salts of the unsaturated aliphatic dicarboxylic acids, containing two more carbon atoms per molecule than the dimers from which they are produced. In the case, for example, where butadiene is the starting aliphatic diolefin, there results by such a method 7 n the selective production of C unsaturated aliphatic dicarboxylic acids.

The unsaturated diacid products find use as chemical intermediates, and are valuble in the preparation of polymers and copolymers, plasticizers, and drying oils. They, as well as certain derivatives, are useful in esters, polyester and polyamide resins and, generally, as chemical intermediates.

In addition, the unsaturated diacids or their salts or other derivatives can be hydrogenated at the double bonds to yield the corresponding saturated compounds, particularly the saturated diacids. This also affords a convenient and accurate way to identify structures of the intermediate products. For example, the disodiooctadiene product obtained from reaction of butadiene with sodium by a process embodied herein ultimately yields a practically quantitative mixture of sebacic acid, 2-ethylsuberic acid, and 2,2-diethyladipic acid upon subjecting the disodiooctadiene product to carbonation, hydrogenation and acidification.

As a suitable method for preparation of dispersions suitable for practice of this invention and which dispersions of the aforedefined particle size characteristics are believed to be novel, an inert hydrocarbon is placed in a suitable vessel with the appropriate amount of alkali metal (sodium), suitable materials useful as the inert hydrocarbon being saturated dibutyl ether, n-octane, isooctane, toluene, xylene, naphthalene, n-heptane, straight run kerosenes, etc. The mixture is then heated in a surrounding bath or otherwise until the sodium has melted M. P. 97.5" C). A suitable high speed agitator is then started and, preferably, an emulsifier consisting, for example of /2% (based on sodium) of the dimer of linoleic acid is added. After a short period of agitation, a dispersion of sodium particles in the range of 5-15 microns is normally obtained (i. e., Normal dispersions illustrative of finely dispersed sodium which, for obtaining substantial yields of the desired dimerized products, require use of an activating agent and/or attrition agent as aforedescribed in reaction with the diolefin).

A suitable mill, such as a homogenizer, is preheated by placing a small amount of inert hydrocarbon (e. g., mineral spirits) in the retention pot and running the mill until the liquid reaches a temperature in the range of 105-1 C. When such a temperature has been reached, the above described preformed Normal dispersion is added to the retention pot while the mill is continued in operation. Preferably, the vehicle for the dispersion and the small amount used for pre-heating the homogenizer mill are calibrated and accounted for so that a sodium concentration of from about 10 to about 60%, and preferably -50%, is maintained for preparation of final finished dispersions of highly suitable stability characteristics. The selective dispersing aid or aids that are employed can be incorporated by adding only a portion of the total amount thereof to the mixture while forming addition thereto of the Normal dispersion. On the other hand, all of the dispersing aids can be added to the preformed dispersion before its addition to the homogenizer equipment. By such a two-step process, the Normal dispersions can be converted to dispersions in which the maximum size of the particles of sodium do not exceed about 3 microns with an average micron size of l and less and which, for purposes herein are designated as the Fine dispersions utilized in describing specific embodiments of the invention. For preparation of such dispersions, other dispersion units, including those of the ultrasonic type, may be used and which operate successfully with either a preformed dispersion or molten sodium feed.

In order to further describe the invention, the following tabulation sets forth results obtained by carrying out embodiments of the invention and, for comparison purposes, results obtained by carrying out the process under identical conditions except for use of an alkali metal dispersion which, though of low average particle size, did not contain the aforestated amount of particles below about 5 microns in size required for practice of this invention.

Although the invention is illustrated with use of specific embodiments using sodium as the alkali metal, dimethyl other as the reaction medium, and butadiene as the olefin reactant and mineral spirits as the suspension medium, it should be understood that their use is for illustrative and not limitative purposes as the process embodied herein may be carried out with use of other alkali metals, olefins, reaction mediums, suspension mediums and other reaction conditions as is more broadly described hereinbefore.

The sodium dispersions employed in the runs for which data are shown consisted of a Normal dispersion itself, a Fine dispersion sodium) prepared as aforedescribed in mineral spirits, and controlled mixtures of such dispersions, the particle size characteristics of which were determined by visual examination with a microscope hav ing a calibrated eyepiece. The reactions, for which data are set forth in the following tabulation, were carried out in a stirred reactor having a gas inlet tube and a reflux condenser vented to a nitrogen atmosphere. The reactor system was purged with nitrogen and charged with 3 liters of 'dimethyl ether, followed by addition of the sodium dispersion (1.1 g. atoms). Butadiene (l g. mole) was then passed into the reactor with stirring over a thirty minute period at a temperature of about C. Following completion of the reaction, the reaction mixture was carbonated by pouring it upon an excess of solid carbon dioxide. After evaporation of excess carbon dioxide, dimethyl ether and alkylate, the remaining solid product was acidified with hydrochloric acid, and the acidified product distilled. The distillate obtained was, in each case, analyzed for content of C aliphatic diacids and the yield thereof for each run is set forth in the tabulation below, the yield being based on the amount of butadiene employed in the reaction.

Percent Sodium Dispersion Fine Dispersion Normal Dispersion Average Percent of Parti- Percent of Parti- Yield of Run N0. Average=12 microns Particle cles of 5 or less cles over 15 mi- 010 diacids Maximum Particle size= size microns crons based on Average=1 micron 30 microns butadiene Maximum Particle Particles over 15 microns= size=3 microns not more than 10% Particles of 5 microns or below=not more than 10% 0 100 12 not more than 10.. not more than 10.. O 25 75 9. 25 7.5 7 35 8.1 38 50 50 6 100 1 87 the Normal dispersion and adding the remainder to the initial diluent charge in the homogenizer mill prior to As is apparent from the data in the foregoing tabulation, use of the sodium reactant in the form of a Normal dispersion of 12 micron average (run No. did not result in formation of disodiooctadienes in view of the failure to obtain C aliphatic diacids upon carbonation and acidification of the reaction mixture. Moreover, as shown for run No. 6, wherein the sodium dispersion was the defined mixture of the Fine dispersion and Normal dispersion, but in which the amount of less than 5 micron particles was on the order of only about 30%, substantial yields of the C diacids did not occur. However, as shown for the remaining runs, Nos. 7-9, the use of a sodium dispersion in which substantially more than 30% of the particles were of less than 5 microns, resulted in markedly improved yields. For example by plotting the data using a yield of C diacids as the ordinate and per cent of particles below 5 microns in the dispersion as the abscissa, a sharp increase in yield of C acids is revealed when the sodium dispersion contains substantially more than 30% of less than 5 micron size particles.

Most preferred practice of the invention is illustrated by the results shown for run No. 9 wherein, by use of a sodium dispersion devoid of particles over about 3 microns in size, an 87% yield (based on butadiene) was obtained, i. e., a yield comparable to those obtained by essential use of activating agents and/ or attrition agents with sodium dispersions which, though of relatively fine particle size, do not contain the aforedefined amount of more than about 30% of particles below 5 microns for practice of this invention.

In the runs carried out in accordance with this invention whereby the C diacids were produced in substantial yields, analysis of the diacid mixtures, following hydrogenation thereof in the presence of nickel hydrogenation catalyst, yielded mixtures of sebacic acid, 2-ethylsuberic acid and 2,2 diethyladipic acid, generally in a ratio of 3.5:5:1 parts by weight, respectively, thus evidencing that disodiooctadienes, formed by reaction of butadiene with sodium, were produced in high yield and that such disodiooctadienes, upon carbonation and acidification, yielded the C aliphatic diacids that were precursors (before hydrogenation) of sebacic acid, Z-ethylsuberic acid and 2,2-diethyladipic acid. Such individual acids may suitably be isolated by methods disclosed in co-pending application S. N. 382,456.

Over and above the decided advantages that result from the present invention, including the eifecting of the de sired dimerization of the diolefins with alkali metals without need for resort to use of activating agents, attrition agents, etc., and the resulting substantial simplification of the process both as to the metalation reaction and subsequent processing operations for conversion of the dimerized products to valuable derivatives and the recovery thereof in substantially pure form, the use of alkali metal dispersions, as embodied for use herein, obviates or substantially minimizes the agglomeration or lump-forming tendency of dispersed sodium, the occurrence of which requires, while carrying out reactions therewith, more frequent shutdowns due to plug-up of equipment, transfer lines, etc. Thus, based on studies of agglomerate-forming tendencies of dispersed sodium in a process as embodied herein, use of the sodium as a dispersion of the required particle size characteristics for practice of this invention has resulted in obviating balling or agglomeration of sodium for much longer period of time than in the case of carrying out the reaction with Normal sodium dispersions, as aforedefined even in the presence of attrition agents such as sodium chlorides and sodium sulfate.

While there are above disclosed but a limited number of embodiments of the process of the invention herein presented, it is possible to produce still other embodiments without departing from the inventive concept herein disclosed, and it is desired therefore that only such limitations be imposed on the appended claims as are stated therein.

What is claimed is:

1. A process for selective formation of dialkali metal dimers of a conjugated aliphatic diolefin which comprises reacting a conjugated aliphatic diolefin with finely divided particles of an alkali metal dispersed in an ether reaction medium from the group consisting of aliphatic monoethers having a methoxy group and an oxygen to carbon ratio of not less than 1:4 and polyethers derived from an aliphatic polyhydric alcohol having all the hydroxyl hydrogen atoms replaced by alkyl groups and mixtures thereof, said finely divided alkali metal being comprised of particles of which more than about 30% are less than about five microns in size and the average particle size of the alkali metal particles is substantially less than eight microns.

2. A process for selective formation of dialkali metal dimers of a conjugated aliphatic diolefin which comprises reacting a conjugated aliphatic diolefin with finely divided particles of an alkali metal dispersed in a liquid ether reaction medium from the group consisting of aliphatic monoethers having a methoxy group and an oxygen to carbon ratio of not less than 1:4 and polyethers derived from an aliphatic polyhydric alcohol having all the hydroxyl hydrogen atoms replaced by alkyl groups and mixtures thereof, said finely divided alkali metal being comprised of particles of which more than about 30% are not more than about three microns in size and the average particle size of the finely divided alkali metal is not more than about six microns.

3. A process, as defined in claim 2, wherein the diolefin contains from four to eight carbon atoms.

4. A process, as defined in claim 3, wherein the diolefin is butadiene.

5. A process, as defined in claim 2, wherein the diolefin is butadiene, the alkali metal is sodium, and the reaction is carried out at a temperature of below about 0 C.

6. A process, as defined in claim 2, wherein the average particle size of the dispersed alkali metal is not in excess of about one micron.

7. A process, as defined in claim 2, wherein the alkali metal dispersion is devoid of more than 10% of particles of over about 15 microns in size.

8. A process, as defined in claim 2, wherein the alkali metal is sodium, the diolefin is butadiene, substantially all of the dispersed sodium particles are not more than about three microns in size, the average particle size of the dispersed sodium is not more than about one micron, the reaction is carried out at a temperature not in excess of about 0 C., and the ether reaction medium is dimethyl ether.

References Cited in the file of this patent UNITED STATES PATENTS 2,352,461 Walker June 27, 1944 2,579,257 Hansley et al Dec. 18, 1951 2,773,092 Carley et a1 Dec. 4, 1956 2,799,705 De Pree et al July 16, 1957 OTHER REFERENCES Hansley: Ind. and Eng. Chem., vol. 43, No. 8, pages 1759-1766, pages 1759, 1760 only needed. 

1. A PROCESS FOR SELECTIVE FORMATION OF DIALKALI METAL DIMERS OF A CONJUGATED ALIPHATIC DIOLEFIN WHICH COMPRISES REACTING A CONJUGATED ALIPHATIC DIOLEFIN WITH FINELY DIVIDED PARTICLES OF AN ALKALI METAL DISPERSED IN AN ETHER REACTION MEDIUM FROM THE GROUP CONSISTING OF ALIPHATIC MONOETHERS HAVING A METHOXY GROUP AND AN OXYGEN TO CARBON RATIO OF NOT LESS THAN 1:4 AND POLYETHERS DERIVED FROM AN ALIPHATIC POLYHYDRIC ALCOHOL HAVING ALL THE HYDROXYL HYDROGEN ATOMS REPLACED BY ALKYL GROUPS AND MIXTURES THEREOF, SAID FINELY DIVIDED ALKALI METAL BEING COMPRISED OF PARTICLES OF WHICH MORE THAN ABOUT 30% ARE LESS THAN ABOUT FIVE MICRONS IN SIZE AND THE AVERAGE PARTICLE SIZE OF THE ALKALI METAL PARTICLES IS SUBSTANTIALLY LESS THAN EIGHT MICRONS. 